L-3,4-dihydroxyphenylalanine (L-DOPA) is the mainstay of therapy for Parkinson's disease (PD). Chronic L-DOPA therapy is limited, however, by the development of motor response complications, such as progressively shorter duration of improvement in akinesia (wearing-off) and the appearance of L-DOPA-induced abnormal involuntary movements. Innovative methods of sustained and localized central nervous system (CNS) dopamine delivery may further optimize L-DOPA therapy. Such methods are being explored clinically by CNS transplantation studies with fetal dopaminergic neurons and experimentally by neuronal stem cell implants and gene therapy. Our studies during the past funding cycles have defined optimal sets of genes necessary for dopamine replacement using ex vivo gene therapy using genetically modified fibroblasts. We also developed rat behavioral models that are relevant to the akinesia of PD patients. Using akinesia behaviors, we have noted that lesion severity has a major influence on the shortening of the response duration with minor contribution by the chronic intermittent L-DOPA therapy. Therefore, studies proposed in this continuing renewal application will determine the optimal parameters of gene therapy to improve akinesia and minimize and prevent motor response complications. We will use adeno-associated virus vectors to deliver tyrosine hydroxylase and guanosine triphosphate (GTP) cyclohydrolase 1 genes. The optimal combination of anatomical targets for gene therapy to improve akinesia will be defined by examining the effects of gene therapy delivered to basal ganglia structures, such as subthalamic nucleus, substantia nigra par reticulata, that receive dopaminergic inputs, in addition to the striatum. The optimal timing to initiate dopamine replacement gene therapy to forestall development of motor response complications will also be examined. These results will have significant implications beyond dopamine replacement gene therapy proposed here and guide other therapies such as fetal dopaminergic cell transplantation, neurotrophic factor therapy, stem cell therapy, and other CNS targeted delivery systems.